A problem exists as residential telephone station equipment has become more complex. Telephone line DC power has proven insufficient to power the features available in the latest commercial offerings of residential feature telephone station sets. A feature telephone station set is a telephone set having a data processor and providing a host of features. These features may include among others, repertory dialing, alpha-numeric display, user programming and hands-free loudspeaker operation. Frequently, transformers and rectifiers operating off alternating current power or batteries are provided with such telephone sets at a residence to alleviate the power problem.
Powering the telephone station sets with rectified alternating current power can cause undesirable noise which can be induced into the telephone communications path. Using batteries, on the other hand, has brought about a different problem, namely, that of monitoring closing the loss of battery power and having to periodically replace the batteries.
One solution to the power consumption problem has been to carefully apply the power resources available. For example, R. W. Christian and W. G. Kutzavitch, in U.S. Pat. No. 4,279,020, teach that a microprocessor of a telephone set may be powered up and powered down responsive to an input received from a data input device such as a keyboard. In a data processor-based feature telephone set, it is the data processor which consumes most of the battery power. Thus, Christian and Kutzavitch teach that the data processor can be powered up only when it is needed. For power-down, the data processor actuates a power-down subcircuit which removes power from the data processor. Meanwhile, battery power is continuously provided to the volatile random access memory of the data processor.
Ferguson, U.S. Pat. No. 4,315,162, discloses a reserve power supply for data processing systems which comprises first and second sources of direct current power. Under processor control, the sources may be connected in parallel or in series in order to increase their voltage output. Furthermore, Ferguson discloses a circuit for converting the DC voltage from one supply into a plurality of voltage levels.
Both solutions fail to eliminate a requirement for locally provided battery or rectified alternating current in data processor-based feature telephone station apparatus. There remains a requirement for improved line power control means, the objective being a wholly line-powered feature telephone station set.